1. Field of the Invention
This invention relates to a device for controlling the valves, headgates, or zonal pumps which supply irrigation water based upon the sensed needs of the area to which water is intended to be supplied and on the availability of water as determined by pressure or level.
2. Description of the Related Art
An irrigation system distributes water from a source, such as a reservoir or an aquifer, to a point of utilization.
Several techniques are commonly utilized to move the water, viz., gravity flow from a reservoir into and through canals and ditches; gravity flow from a reservoir into and through a closed system of main-line and branch pipes, wherein the water is pressurized through subsequent decreases in elevation; pumping from a reservoir, canal, or river into a closed system of main-line and branch pipes, wherein the water is pressurized through the force exerted by the pump; and pumping from an aquifer into a closed system of main-line and branch pipes, wherein the water is pressurized through the force exerted by the pump.
Areas to be irrigated are generally divided into zones. Zones are established such that throughout any given zone there is a uniform water requirement as well as a device for applying water uniformly.
In the case of an open gravity-flow system, for each zone the reservoir typically may either lead to a canal from which a ditch goes to the zone, or the ditch may go directly from the reservoir to the zone. With either option, the flow of water into the ditch for a given zone is regulated by a headgate, i.e., a headgate between the canal and the ditch or between the reservoir and the ditch, or a pump, designated the zonal pump, which lifts water from the canal or reservoir to the ditch. Generically, it may be said that the headgate or zonal pump is between the source and the ditch. When the headgate is opened or the zonal pump is actuated, water flows into the ditch and, consequently, to the zone.
When a pressurized main-line pipe is utilized, for each zone a branch pipe normally goes from the main-line pipe to the zone. A valve connects the main-line pipe to the branch pipe. When the valve is opened, water flows into the branch pipe and, consequently, to the zone. If the zone is sufficiently higher than the main-line pipe, however, it may be necessary both to open a valve and to actuate a zonal pump.
The purpose for applying water to the zone may be agricultural or industrial. Agricultural goals include stimulating plant growth, avoiding dryness, protecting against excessive heat, and precluding freezing. Industrial uses comprise the treatment of waste water and the leaching of minerals.
An irrigation system may be monitored and controlled manually. This necessitates having an individual observe the conditions in each zone. When the individual determines that a zone requires irrigation, such individual ascertains whether adequate water is available. If it is, this individual then opens the appropriate headgate or valve and does not close it until either learning that the needs of the zone have been met or that insufficient water remains in the source to continue supplying water to the zone.
As the demand for, and prices of, water and the cost of energy to operate pumps have increased, there has been a corresponding trend to automate the operation of irrigation systems.
U.S. Pat. No. 4,791,948 of John J. Bayat explains the use of a timer to regulate, with no sensory input, the operation of associated sprinklers.
A variety of patents have gone beyond this simple concept to detect physical conditions--principally moisture in the soil--and use this data to influence the operation of the irrigation system.
A sensor containing logic to prevent a valve from supplying water to a sprinkler located near the sensor when moisture in the soil exceeds a preset value was introduced in U.S. Pat. No. 4,852,802 of Jerry R. Iggulden and Donald A. Streck. This device, however, had no means for communicating with other such controllers.
Centralized control seems to provide the desired communication in all other patented devices that utilize sensory detection in the automated operation of an irrigation system.
The invention in U.S. Pat. No. 4,875,498 of T. Arthur Andrews and D. Glenn Gibson also concentrates on a detector for soil moisture which will preclude watering when the moisture in the soil is too high. It operates only when instructed to do so by a central controller which can, additionally, override the effect of the detector. The central controller is disclosed, but not claimed, to be actuated by a timer switch, a temperature or freeze switch, or a light-responsive switch.
U.S. Pat. No. 4,545,396 of Richard N. Miller and K. Bruce Ray deals with a system which employs detectors to measure impedance of the soil. Reactance is said to be indicative of the moisture in the soil; resistance, of the salinity in the soil. Information from the detectors is sent to a measuring device and a control device. The disclosure indicates these would be centrally located; but the claims could be read such that each zone would have its own measuring device and control device, in which case there would be no communication among such devices for different zones. Reactance measurements would be used to determine when to start and stop watering; resistance measurements, when to add fertilizer to the water.
Similarly, the system associated with U.S. Pat. No. 4,548,225 of Dwight J. Busalacchi uses a sensor to measure soil moisture and initiates as well as precludes the flow of water in accordance with preset values. The automatic control means is connected to the main valve for each field that is to be watered. The claims suggest, and lines 35 through 37 in column 3 of the disclosure clarify, that the control means is centralized.
Again, although the claims do not indicate explicitly whether control is centralized, the irrigation control system in U.S. Pat. No. 5,023,787 of Rene H. Evelyn-Veere would seem to necessitate centralized control; and the disclosure, on lines 20 through 24 of column 4, discusses a basic automatic irrigation control system involving a central computer. The invention, moreover, ". . . controls irrigation schedules to regulate pump operation to provide an approximately level demand for pump capacity over a complete watering cycle . . ." without exceeding flow limitations of the distribution system to assure that ". . . water pressures and actual flow rates would [not] be diminished." And the system is capable of considering a weather evapotranspiration value which is provided by the operator of the system and which is representative of the then current weather conditions.
The irrigation control system in U.S. Pat. No. 5,048,755 of Graeme C. Dodds is clearly disclosed to have a central computer which can communicate with an encoder by telephone, radio waves, microwaves, or fibre optics. The encoder has a back-up memory and, to reduce the extensive quantity of wiring associated with centralized irrigation control systems, uses only two wires (or optical fibres) to send coded signals to the devices that activate valves. Each such device is, through a decoder, activated by its own code. In the preferred embodiment, the central computer also receives data from a weather station; and watering cycles are commenced when a condition based on time or weather is reached. Additionally, a flow transducer and a pressure transducer in the main pipe provide data to the central computer; and local field conditions such as moisture, rain, or wind may be sensed and provided to the computer. When a watering cycle is commenced, valves continue to be opened ". . . until the actual flow rate, as measured by the flow transducer . . . , substantially reaches the available design flow rate determined by factors such as the diameter of the supply pipe . . . , whilst maintaining a minimum predetermined design pressure as sensed by the pressure transducer . . ."
Although this last patent partially solved the problem of the extensive wiring required for communication among a central control unit and local control devices, it did not eliminate this difficulty. Centralized control, moreover, complicates design as well as installation of an irrigation control system and interposes significant obstacles to altering the system once it has been built.